During the operation of large electrical machines such as motors and generators a substantial amount of heat is generated in the active parts i.e. the stator and the rotor of the machines. The excess heat has to be transferred out of the machine in order to avoid malfunction because of overheating. Therefore, large electrical machines are provided with cooling systems that implement the heat transfer function.
Cooling systems may comprise a great variety of technical principles and practical solutions depending on the amount of heat, access to a cooling medium, requirements of the machine, etc. One typical machine requirement is that the interior of the machine housing should not be in direct contact with the ambient air. Some of the conventionally used cooling principles in the case of such closed housing are disclosed in the following patent publications.
U.S. Pat. No. 6,700,237 discloses in the embodiments of FIGS. 1 to 8 an electrical machine in which the machine housing is provided with cooling fins such that the housing itself functions as a heat exchanger to the ambient air. In further embodiments U.S. Pat. No. 6,700,237 discloses external heat exchangers where the air circulated through the interior of the machine is cooled.
U.S. 2002/0149273 discloses an electric motor comprising an internal cooling air circuit and an annular heat exchanger with ducts for a cooling liquid. U.S. 2002/0149273 does not thoroughly describe the cooling liquid circuit outside of the motor housing, but in a typical arrangement the ducts are connected to an external water pipe network.
U.S. Pat. No. 5,844,333 discloses an electric motor air cooler using an air-to-air heat exchanger. The air cooler comprises an ambient air fan for circulating ambient air over the heat exchanger, and an internal fan for circulating the air inside of the motor housing and over the heat exchanger.
U.S. Pat. No. 6,499,532 discloses an electric motor cooling system comprising a first blower for circulating the air inside a motor housing and over a first half of a heat pipe array, and a second blower for forcing the ambient air over a second half of the heat pipe array.
Some of the aforementioned cooling principles have the drawback that they assume the use of an external cooling medium such as water. While it often is burdensome to install the water piping to the machine, in some circumstances there is not even access to external water. The remaining conventional cooling principles have the drawback that the efficiency is poor and the dimensions of the resulting heat exchangers are huge compared to the machine dimensions.